1. Field of the Invention
The present invention relates to a cooling device for the pressing tools of an upsetting press for the width reduction of rolled material, particularly of the width of slabs in hot-rolled wide strip roughing trains. The upsetting press includes two tool carriers which are arranged on both sides of the slab edges. The tool carriers receive the pressing tools and are moved relative to each other. The invention also relates to a method for operating the cooling device.
2. Description of the Related Art
The pressing tools of an upsetting press for reducing the width of slabs in hot-rolled wide strip roughing trains are subjected to extremely high mechanical and thermal loads. Since the temperature of the hot slab entering the upsetting press is approximately 1250.degree. C., and since the pressing tool is subjected during pressing to the direct heat contact with the slab and also to the radiation heat emanating from the hot slab, the pressing tool must be cooled in order to obtain a service life of the tool which is operationally acceptable.
In a known device for changing the cross-section of hot slabs received from a slab casting machine as disclosed in German Offenlegungsschrift 25 31 591, it is proposed to cool the pressing tools by means of an internal circulation of a medium, wherein it is ensured that the working sides of the tools are at or close to the highest permissible temperature in order to remove the smallest amount of heat from the slab and to avoid an excessive wear of the tools.
However, the present invention starts from the finding that the heat flux from the front edge of the pressing tool which comes into contact with the hot slab to the portions of material of the pressing tool which define cooling ducts for reasons of strength, takes place too slowly and, therefore, an internal circulation of a cooling medium is not capable of removing sufficient heat from the pressing tool with the result that the temperature of the tool levels out after a certain period of operation at a temperature which is substantially higher that the highest permissible temperature. Arranging the cooling ducts in the tool at a slight distance away from the pressing surfaces to be cooled has the result that the pressing surfaces of the pressing tool can only be finished to a limited extent and that, therefore, the service life of the pressing tool is reduced to an extent which is economically unacceptable. For reasons of cost, it is also not acceptable to coat the pressing surfaces of the tool with such high-grade materials, for example, by build-up welding, which are capable of withstanding the extremely high operation temperature. In addition, such high-grade metal alloys require technically very difficult finishing of the pressing surfaces.